Though I'm not sure about other manufacturers, I haven't hear of any issues concerning CA's folding stock for their G36 prolines. Upgrade options are plentiful though not compared to an M4 platform. I think all of CA's G36s fits a mini type battery in the handguard but using a PEQ battery case works quite well or you can get the G&P sniper style retractable buttstock that fits a custom battery with, I think, 3300mah. And I haven't had issues of my CA36 (full length) snagging on anything.
Downside, G36 mags are pretty thick...roughly 1.5x thicker then standard M4 mags. I found pouches designed for G36 mags are hard to come by, usually designed into a vest and I like running a MOLLE vest with different setups but at least as mentioned above, you can get a magwell converter to use M4 mags. May not be the most realistic if that matters to you or look sexy but its practical.
"Hey I'm the first one to say its a great country but its a straaaaange culture. This is a place where gun store owners are given a list of stolen credit cards but not a list of CRIMINALS and MANIACS. And now they're thinking of banning toy guns...AND THEY'RE GONNA KEEP THE F**KING REAL ONES!"
-George Carlin 1937 - 2008 (RIP buddy)